A world is a particular sort of thing. Most worlds are either outwards facing or inwards facing, and the majority are inwards facing.

Outwards-facing worlds are rare things like Tabrix or Sabhaxlia--fully enclosed gods, able to exist on their own even in the Not, requiring nothing but themselves for context. Unlike a character, which needs an author to be able to function, outwards worlds are author-characters rolled up in one. When they exist inside another world, there's this SPACE between their shell and the world itself, where there's really very little interaction other than what they agree to. Because of that, outwards-facing worlds are terrifyingly powerful to any character-level person dealing with them, because anything you DO to them, the outward world HAS to consent before it can affect them, at all, whatsoever. (This is a simplification, in reality the host-world proposes the Story as a pressure to the guest-world, and it's less that consent has to be given and more that refusals can be made by closing their gates to the external Story presented by the host-world.) Of course, the outwards-facing world has to make allowances, has to not strain verisimilitude, has to allow things to affect them, or find themselves just, so isolated from that world they pop out. Breaching verisimilitude means you kind of glide off the world you no longer fit into at all like oil on water, and you (usually) end up at x0y0z0, the City in the Middle, which is technically also a world but runs on her own rules.

But the point is, outwards-facing worlds are like a sphere with all their stuff on the outside. All the Story production happens on the surface and from external points. Actual honest-to-goodness outwards-facing worlds--not metafictionally active entities, which are relatively common, but the worlds themselves, which are actually pretty rare--they're "hollow" on the inside. The inside actually contains their metafictional organs--the I-Am, which is the unassailable "canon" of the character especially, and the actual guts that process Story--but the point is, outwards facing worlds face outwards, and you can talk to them.

Inwards facing worlds are far, far, far more common. Most aren't even sapient or sentient, having divided their original Identity into their Heirs, and then into Successors, and into all the little nitty-gritties of the world where you're mostly interacting with a non-sapient Story machine on the higher levels, unaware of what it's doing and just working off of rules programmed into it at the start of its time. Some inwards-facing worlds actually do have true world consciousnesses, where the world itself as a whole has ideas and thoughts and an Identity. Usually lower-verisimilitude worlds are like that, where they try a bit less hard to hide that they're fictional.

Most inwards-facing worlds are just floating in the Not, visible as points of light, masses of Story, slowly burning out against the Voiding until they're finally consumed by O. It's very, very hard to just, sail to another world, and there are a million better tricks to go world to world, and because it's in the Not there's no coherent distance between them, it's a mess. But you get to an inwards-facing world, and there's this barrier of Story, and if you can slip through then suddenly the world provides you with context, and you go from "seeing" a huge expanse of metaphorical pages to being inside a living real world.

Then you have.

Hecking.

Worlds like Under Watchful Is, which is a double-sided hecking world. Inside her is a massive universe filled with millions and millions of lives. Countless stories are carried out every moment. People are born and die and dreams are broken and achieved and inside her everything is real and meaningful and the world is massive and great.

On the outside she's just this hecking deer that's hanging out with the mother of the thing that tried to eat her when she was a baby. At a slime bar, where you drink jello shots made from slime bartenders. They're probably going to bang.

The world you are in might be having sex with another world right now and you'll never know it.